1. Field of the Invention
The present invention relates to direct oxidation of methyl halides by a methylotrophic bacterium in a bioreactor.
2. Brief Description of the Related Art
Use of methyl bromide (MeBr) as a quarantine, commodity and structural fumigant is under scrutiny because its release to the atmosphere contributes to depletion of stratospheric ozone and it poses a risk to human health.
Approximately 35% of the methyl bromide (MeBr) sold in the United States is used for fumigating structures for pest control or for disinfesting commodities and harvested crops prior to shipment or sale (see e.g., Kurylo, M. J. et al. (1999), Short-lived ozone-related compounds, in Albritton G. M., Watson, R. T. and Auchamp, P. J. Eds. Scientific assessment of ozone depletion (1998), 2.1-2.37 Report No. 44, World Meteorological Organization, Geneva). In these uses, high levels of MeBr, generally between 17 g/m3 to 42 g/m3, are directly vented to the atmosphere following exposure to structures or commodities in closed containers. MeBr has a residence time of greater than 8 months in the troposphere allowing a significant fraction to be transported to the stratosphere where MeBr facilitates the destruction of ozone. The major use of MeBr, pre-plant field fumigation being 65% of sales, is currently being phased out by international agreement, particularly through the Montreal Protocol, as amended, and as a consequence of the 2001 United States Clean Air Act. Another methyl halide, Mel, is highly toxic to humans.
Several strategies have been proposed for capturing MeBr from the waste stream of commodity and structural fumigations followed by subsequent recycling or destruction, such as adsorption of MeBr on zeolite or on activated charcoal. Although approximately 80% of the treated MeBr may be recovered using a single bed or cartridge of activated charcoal adsorber, emissions of as high as 200 to 500 ppm MeBr (0.9 to 2.1 g/m3) may result from this practice.